What is tick-borne relapsing fever?

Tick-borne relapsing fever refers to a type of illness caused by the bacteria Borrelia miyamotoi carried by ticks.  In San Mateo County, the ticks that carry bacteria that cause this illness are Ixodes pacificus, the western black-legged tick.  It is closely related to the bacteria that causes tick-borne relapsing fever.  The infection is treatable with antibiotics.  A person who has been bitten by a tick and develops symptoms of tick-borne relapsing fever should see their physician.

How is tick-borne relapsing fever transmitted?

Tick-borne relapsing fever is transmitted by the bite of an infected tick.

If I get bitten by a tick, will I get tick-borne relapsing fever?

Most ticks are not carrying B. miyomotoi bacteria.  In 2016, Ixodes pacficus ticks collected from parks in San Mateo County had an infection prevalence ranging from 2.0% to 0%.   Checking for ticks after hiking or camping and removing ticks promptly will reduce the risk of acquiring the disease.

What are the signs and symptoms of tick-borne relapsing fever?

• Fever
• Headache
• Joint/body pain
• Malaise
• Chills

Symptoms will vary from person to person.

For more information visit the CDC website.

Page last reviewed: February 20, 2025